Idea: Use custom pcase form to aid error handling

[alphapapa]

Not sure about the specifics, but it might be nice to use a custom pcase-defmacro expander to help with writing error handling in plz-related code.

cc: @josephmturner

[josephmturner]

What kind of API would be useful for handling errors with pcase? One peculiarity with plz error handling that I've noticed in hyperdrive.el is that synchronous code deals with full errors like this: ;; (plz-error "Curl error" #s(plz-error (7 . "Failed to connect to host.") nil nil)) ;; (plz-error "HTTP error" #s(plz-error nil #s(plz-response 1.1 404 ((content-type . "text/plain;charset=UTF-8") (date . "Thu, 07 Sep 2023 02:15:36 GMT") (connection . "keep-alive") (keep-alive . "timeout=5")) "") nil)) whereas asynchronous code deals with just the plz error struct that might be passed as the DATA argument to `signal`. Perhaps the pcase-defmacro could help avoid the awkward use of `caddr` to get the plz-error struct before it can be destructured, e.g. <https://git.sr.ht/~ushin/hyperdrive.el/tree/e88112f2d2e44b7450450679bff183f33ba9519a/item/hyperdrive-lib.el#L396>.